A negative-pressure type booster device is provided with, for example, a housing formed of a front shell and a rear shell, a movable partition wall which partitions the interior of the housing into a negative-pressure chamber on a front side and a variable pressure chamber on a rear side, and a main body which opens or closes the variable pressure chamber to atmospheric air. When the variable pressure chamber is opened to the atmospheric air, the movable partition wall is pressed toward the negative-pressure chamber side by a differential pressure between the variable pressure chamber and the negative-pressure chamber, and moves forward. When the variable pressure chamber and the negative-pressure chamber communicate with each other, the differential pressure between the variable pressure chamber and the negative-pressure chamber decreases, and pressing force to a forward movement side of the movable partition wall decreases. Therefore, the negative-pressure type booster device is provided with a negative-pressure valve which allows the communication between the variable pressure chamber and the negative-pressure chamber and blocks the communication, and an atmospheric valve which allows the communication between the variable pressure chamber and the atmospheric air and blocks the communication. The negative-pressure valve and the atmospheric valve have a valve part and a valve seat, and are opened and closed by contact and separation of both of them. Such a negative-pressure type booster device is disclosed in, for example, Japanese Unexamined Patent Publication No. 2009-23506.